Regex to Trim Trailing Whitespace from Lines

Trim Trailing Whitespace

Trailing whitespace pollutes diffs and breaks some parsers. Most editors strip it on save, but regex is useful for batch cleanup or one-off scripts.

Trim Trailing Whitespace from Every Line

str.replace(/[ \t]+$/gm, "")

The m flag makes $ match at every line ending. The character class [ \t] covers spaces and tabs without touching the line terminator itself.

Trim Both Ends of Each Line

str.replace(/^[ \t]+|[ \t]+$/gm, "")

Trim Only the Whole String (not per-line)

str.replace(/^\s+|\s+$/g, "")

This is equivalent to String.prototype.trim().

Trim Only Leading or Only Trailing

str.replace(/^\s+/, "")  // trimStart
str.replace(/\s+$/, "")  // trimEnd

Tested Examples

Input	Per-Line Trailing Trim
"hello "	"hello"
"line1 \nline2\t\t"	"line1\nline2"
" preserved\n also preserved"	unchanged (only trailing)
"\t\n"	"\n"

Remove Trailing Newlines from a File

str.replace(/[\r\n]+$/, "\n")

Keeps a single final newline (POSIX convention).

Remove Empty Lines

str.replace(/^\s*\n/gm, "")

Practical Recommendation

Pair this regex with a pre-commit hook to keep your diffs clean. Many editors (VSCode, Vim, Sublime) have a one-click "Trim Trailing Whitespace" command. For mass cleanup of an existing repository, run:

find . -name "*.js" -exec sed -i "" -E "s/[[:space:]]+$//" {} +

(macOS sed syntax shown; GNU sed omits the empty quote argument.)

Why It Matters

Trailing whitespace causes:

• Spurious diffs in code review
• "Trailing whitespace" warnings in linters (ESLint, RuboCop)
• Hidden bugs in shell scripts where a trailing space changes argument parsing